Inlet and outlet module for a heat exchanger for a flowpath for working medium gases

ABSTRACT

An inlet-outlet module 108 having both an inlet 58 and an outlet 62 for a heat exchanger system 52 is disclosed. Various construction details which improve the stiffness to weight ratio and the aerodynamic smoothness are developed. In one embodiment, the module 108 is formed of a one piece casting having a lobed mixer 94 at the outlet.

CROSS REFERENCE TO RELATED APPLICATION

This application relates to copending U.S. patent application Ser. No.08/996,009 entitled "Method for Cooling a Component of a Gas TurbineEngine", by Nikkanen et alia, and copending U.S. patent application Ser.No. 08/996,269 entitled "Heat Exchanger System for a Gas TurbineEngine", by Nikkanen et alia.

TECHNICAL FIELD

This invention relates to an inlet outlet module for a heat exchangersystem for ducting cooling air with respect to a fan duct flow path of agas turbine engine.

BACKGROUND

An axial flow rotary machine, such as a gas turbine engine for anaircraft, has a compression section, a combustion section and a turbinesection. In typical fixed-wing aircraft, the engine is mounted in ahousing attached to the wing of the aircraft. The housing is commonlyreferred to as a nacelle. The nacelle both supports and positions theengine with respect to the aircraft. An annular primary flow path forworking medium gases extends axially through the sections of the engine.In aircraft installations, the compression section commonly includes afan section having a bypass duct. The bypass duct provides an annularflow path for secondary working medium gases which extends rearwardlyabout the primary flow path.

A fan rotor assembly in the fan section includes an array of fan bladeswhich extend outwardly across the primary and secondary flow paths. Aplurality of fan exit guide vanes are disposed downstream of the fanblades in the fan duct to receive the relatively cool working mediumgases of the secondary flow path. A plurality of struts are typicallydisposed downstream of the fan exit guide vanes to support the statorstructure and to transmit loads from the engine to its supportingstructure.

During operation, working medium gases are drawn along the primary flowpath into the compression section. The gases are passed through severalstages of compression, causing the temperature and the pressure of thegases to rise. The gases are mixed with fuel in the combustion sectionand burned to form hot pressurized gases. These gases are a source ofenergy to the engine and are expanded through the turbine section toproduce work. A portion of this work is transferred to the compressionsection to drive the fan rotor assembly and its fan blades about an axisof rotation.

The working medium gases in the fan duct have a mass flow which is sixto eight times the mass flow in the primary flow, but with a relativelysmall pressure rise and a modest temperature rise.

Various components in the engine generate heat such as an electricalgenerator or an oil system for providing lubricating fluid to rotatingcomponents in the engine. Oil or another liquid medium is used to carryaway the heat is discharged to maintain operative temperatures of thesecomponents within acceptable limits to cooling air in the fan duct oranother acceptable heat sink, such as fuel for the engine.

One construction using lubricating oil as a means for removing heat andrejecting it to heat exchangers is shown in U.S. Pat. No. 4,151,710,entitled "Lubrication Cooling System For Aircraft Engine Accessory",issued to Griffin et al. The heat is rejected primarily to a heatexchanger extending into the secondary flow path of the engine andsecondarily to a heat exchanger in communication with fuel being flowedto the combustion chamber.

Another example of a cooling system is shown in U.S. Pat. No. 4,474,001,entitled "Cooling System For The Electrical Generator Of A Turbofan GasTurbine Engine", issued to Griffin et al. In the second Griffinreference, this cooling system rejects excess heat to the engine fuelthrough a primary heat exchanger and at low fuel rates supplementaryrejects heat to fan air flowed from the working medium flow path to asecondary heat exchanger which is located remotely from the fan duct. Avalve is used to turn on and off the flow to the fan air (secondary)heat exchanger as required under operative conditions of the engine.

Still another approach is to provide a heat exchanger disposed in acompartment of the nacelle which receives air from two sources: apressurized compartment in flow communication with the compressor of theengine at low power; and, fan air from the fan bypass duct at highpower. Cooling air is flowed from these locations to the heat exchangerand dumped overboard. Valves are required to interrupt the flow from thepressurized compartment at high power and to interrupt the flow from thefan duct at lower power.

Another approach is to provide a flow path to a heat exchanger in a corecompartment which extends from an inlet in the fan duct to an outlet ata downstream location in the fan duct. The outlet is spaced downstream asignificant distance (several feet) such that the outlet is at alocation having a lower static pressure than the inlet to the exchangerflow path. The inlet and outlet are spaced apart by this distance toavoid regions of the fan duct that have the same static pressure, whichcreates an adverse static pressure gradient (zero or slightly negative)between the inlet and outlet.

The inlet protrudes into the fan duct such that it is spaced from theinner wall and the outer wall. The inlet faces the oncoming flow anddrives cooling air through the flow path to the heat exchanger becauseof the difference in static pressure between the inlet and the outlet.The inlet structure is exposed to foreign object damage from ice andother debris which is ingested into the engine and centrifugal away fromthe inner wall to the interior of the fan duct. Such debris impacts theinlet to the heat exchanger and may be carried downstream to the heatexchanger where the debris may strike and block the heat exchanger.

As the cooling air is passed through the heat exchanger, the cooling airreceives heat from components that are cooled by the heat exchanger. Theheated air is discharged into the fan duct at the downstream location.The discharge temperature of the cooling air from the outlet of the flowpath for the heat exchanger may approach unacceptable levels for theadjacent structure. This results from the heat load and level of coolingflow even though the distance between the inlet and outlet creates adifference in static pressure. As a result, a metal shield may beinstalled downstream of the exhaust. The shield is heated, and materialradially inwardly of the shield, such as composite structures, areprotected from the hot exhaust.

The above art notwithstanding, scientists and engineers working underthe direction of applicant's assignee have sought to develop proofcooling systems which avoid complex valving, adverse affects on theefficiency of the operating engine.

SUMMARY OF THE INVENTION

This invention is in part predicated on the recognition that a one piececasting for an inlet and outlet module may be tailored in thickness andshape to correctly reflect flow path contours with minimal wallthicknesses at non-critical locations and maximum thicknesses incritical locations.

According to the present invention, an inlet and outlet module forducting cooling air from a working medium flow path and returning thecooling air to the flow path is formed of a one piece cast constructionwhich includes an inlet, an outlet and flow path walls extending axiallybetween the inlet and outlet to bound the working medium flow path.

In accordance with one embodiment of the present invention, the inlethas a ramp extending forwardly from the inlet and sidewalls which boundthe ramp having decreasing height in an upstream direction and extendingrearwardly from the inlet to the outlet.

In accordance with one detailed embodiment, a circumferentiallyextending surfaces extends from each sidewall of the heat exchangerinlet outlet module to define the inner flow path wall of a fan bypassduct

In one detailed embodiment of the present invention, the thickness ofthe casting material in the area of the inlet opening is at least fourtimes as thick as the material on at least one interior wall of thecasting.

In accordance with one detailed embodiment, the inlet outlet moduleincludes a inlet duct and an exhaust passage, the exhaust passageterminating in a lobed mixer.

A primary feature of the present invention is an inlet and outlet modulefor a heat exchanger which is formed as a one piece casting. Anotherfeature is the absence of steps or gaps on the internal surfaces of themodule which results from the one piece construction. Another feature isa ramp extending forwardly having side walls which extend forwardly fromthe inlet and of decreasing height in the upstream direction.

A primary advantage of the present invention is the stiffness to weightratio of the inlet outlet module which results from its one piececonstruction. Another advantage is the engine efficiency which resultsfrom the precise contouring of the flow paths through the use of acasting and the precise alignment of the inlet and outlet with flowpaths and the avoidance of steps in transition regions which would occurif this were not a one piece construction. In one embodiment, anadvantage is the maintainability of a gas turbine engine which resultsfrom the ability to replace a module with an interchangeable cast moduleand the ability to remove the entire module to provide inspection of anassociated heat exchanger for foreign object damage and blockage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation schematic view of a gas turbine enginepartially broken away to show a heat exchanger system in flowcommunication with a fan bypass duct.

FIG. 2 is an enlarged schematic view of a portion of the engine shown inFIG. 1.

FIG. 3 is an enlarged schematic view of a portion the heat exchangersystem shown in FIG. 2.

FIG. 4 is a perspective view of the inlet and outlet module for the heatexchanger system shown in FIG. 2.

FIG. 5 is an end view taken along the lines 5--5 of FIG. 1 showing theoutlet of the heat exchanger system with a portion of the engine brokenaway for clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a side elevation view of an axial flow rotary machine such asa gas turbine engine 10. The engine is disposed within a housing,commonly referred to as a nacelle 12. The nacelle circumscribes theengine. The nacelle includes compartments for auxiliary equipment suchas a nacelle fan compartment 14 and a nacelle core compartment 16. Thenacelle is adapted to provide an aerodynamic housing for the engine.

The engine has an axis of rotation Ar and is formed of a fan section 18,a compressor section 22, a combustion section 24 and a turbine section26 whose relative locations are shown in FIG. 1. A primary flow path 28for working medium gases extends rearwardly through these sections ofthe engines. The primary flow path enters the engine at the inner mostportion of the inlet to the engine. The nacelle core compartment extendscircumferentially about the engine and is spaced radially inwardly fromthe nacelle fan compartment leaving a fan bypass duct 32 therebetween. Asecondary flow path 34 for working medium gases extends rearwardlythrough the bypass duct and outwardly of the secondary flow path.

The fan bypass duct is bounded by an inner wall 36 and an outer wall 38.The inner wall and outer wall extend circumferentially about the axis ofrotation A_(r) of the engine. A plurality of fan blades (not shown)extend outwardly across the fan bypass duct to pressurize the workingmedium gases in the secondary flow path. A plurality of fan exit guidevanes, as represented by the fan exit guide vane 42, extend radiallybetween the inner wall and the outer wall to receive flow that isdischarged from the fan blades. A plurality of struts, as represented bythe strut 44, are downstream of the fan exit guide vanes. The strutsextend radially between the inner wall and the outer wall and arecircumferentially spaced for providing structural support to portions ofthe engine and to the nacelle.

The fan bypass duct 32 has a discharge fan duct 46 downstream of the fanexit guide vanes 42. The fan discharge duct is characterized by a flowpath having a negligible loss in total pressure along the flow path andcharacterized by a static pressure gradient in the rearward directionthat is substantially non-existent (that is, the static pressures alongthe flow path are substantially equal) or that is rising in staticpressure as a result of contouring of the flow path. At a location 48significantly downstream of the fan exit guide vanes and downstream ofthe fan struts (several feet), the flow is accelerated by a contractingpassage causing the adverse pressure gradient to disappear and becomepositive. A heat exchanger system 52 having a heat exchanger 54 and aflow path 56 for the heat exchanger are disposed in the core compartment16.

FIG. 2 is an enlarged schematic view of a portion of the engine shown inFIG. 1 showing the heat exchanger system 52. The heat exchanger systemis immediately downstream of the array of fan exit guide vanes 42 and isdisposed between a pair of the fan struts 44 which are spacedcircumferentially. The fan struts are broken away for clarity to showthe relationship of the heat exchanger system to the inner wall 36, theouter wall 38 and the secondary flow path 34 for working medium gases.The secondary flow path has lines of flow extending along such wallswhich include flow lines Fd disturbed by the heat exchanger system andflow lines Fu undisturbed by the heat exchanger system with theundisturbed flow lines having a wall flow characteristic (analogous to aboundary layer in axisymmetric flow) having a thickness Bu at each axiallocation.

The heat exchanger system has an inlet 58 and an outlet 62. A compositeliner 64 for noise suppression is immediately adjacent to the outlet ofthe heat exchanger system at the inner wall and extends in thedownstream direction. The distance between the two is less than theheight of the heat exchanger system from the inner wall of the fan duct.

A cavity 66 is disposed in the core compartment of the nacelle. The heatexchanger is disposed in the cavity. The heat exchanger has an inlet 68and an outlet 72 for the cooling air flow path 56. A flow path 74 for aworking medium fluid is in flow communication with the heat exchanger.The hot fluid is in flow communication with components requiringcooling. Examples of working medium fluids for carrying heat to the heatexchanger are engine fuel and engine lubricating oil which receive heatfrom components through which the working medium passes.

The flow path 56 for cooling air of the heat exchanger system extendsthrough the inlet and outlet of the heat exchanger. The flow path isuninterrupted by valving. The term "uninterrupted" means that the flowpath is continuous under all operative conditions of the engine. As willbe realized, portions of the structure disclosed herein might be usedadvantageously with a system having an interrupted flow path.

The flow path 56 for cooling air is in flow communication through theinlet 58 to the heat exchanger system with the secondary working mediumflow path in the fan discharge duct. An inlet duct 76 extends from theinlet plane P and has a length Lid. The inlet duct has a first (inner)wall 78 and a second (outer) wall 79.

A first radially extending conduit 80 extends in the cavity 66 from theinlet duct 76 to the heat exchanger inlet 68 placing the inlet 68 inflow communication with the inlet duct. The first conduit has aplurality of radially spaced turning vanes 82 which extend from the heatexchanger axially across a portion of the conduit. This leaves theremaining axial portion of the first conduit open to the flow of workingmedium gases in a substantially radial direction and in the axialdirection through the heat exchanger.

The outlet 62 of the heat exchanger system 52 includes a second conduit84. The second conduit 84 extends radially and is in flow communicationthrough the heat exchanger 54 with the first conduit 80. The outletincludes an exhaust passage 86. The exhaust passage has a first portion88 which is in flow communication with the second conduit. The firstportion extends radially outwardly. A second portion extends axiallyrearwardly and terminates in a lobed mixer 92. The lobed mixer has anoutlet section 96 at its end. The lobed mixer is spaced outward by aradial height Ho from the undisturbed flow line Fu at the inner wall 36of the fan duct 46. Accordingly, the outlet section provides at itsinnermost surface a reference surface for locating the undisturbed flowline Fu which is circumferentially spaced from this location.

FIG. 3 is an enlarged view of a portion of the heat exchanger system 52shown in FIG. 2. The system inlet 58 has an inner wall 98 and an outerwall 102. The inner wall of the inlet and the outer wall of the inletlie in an inlet plane P which is perpendicular to the flow (flow path56) entering the inlet. The inner wall and outer wall of the inlet atthe inlet plane P are at the location in which the flow is bounded by awall in the outward direction (the outer wall) and bounded by a wall inthe inward direction (the inner wall). This section of flow is commonlyreferred to as the first covered section of flow. The inner wall extendscircumferentially for the width of the inlet. The inner wall is radiallyinwardly of the undisturbed flow line Fu at the inner wall 36 of the fanduct. The undisturbed flow line is coincident with the inner wall 36 andis spaced radially from the outer wall 38 of the fan duct by a distanceHfd.

The outer wall 102 or lip extends circumferentially as does the innerwall. The outer wall or lip is formed by a first outer surface 104 whichextends circumferentially and which diverges radially from the axis Arof the engine as measured in the downstream direction. The outer wall(lip) has a second inner surface 106 which extends circumferentially andwhich converges radially from the axis Ar in the downstream direction.

The outer wall 102 is spaced rearwardly from and radially outward fromthe inner wall 98 of the inlet 58 by a radial height of the inlet Hi.The outer wall is radially outward from the undisturbed flow line aradial distance Hf. The inlet radial height distance Hi is greater thanthe thickness Bu of the wall flow characteristic. The wall flowcharacteristic is similar to a boundary layer characteristic foraxisymmetric flow and refers to a region of unsteady flow withthree-dimensional aspects adjacent to the inner wall 36. The unsteadynature and three dimensional aspects of the flow results from thelocation of the heat exchanger system 52 immediately downstream of thefan exit guide vanes 42 and between the adjacent fan struts 44. Asdiscussed below, the exposure ratio, aspect ratio, and penetration ratioof the inlet are important parameters for gauging the exposure of theheat exchanger system to potential foreign object damage and the lossesassociated with disturbance of the working medium flow path by the heatexchanger system.

As shown in FIG. 3, the inlet has an exposure ratio to foreign objectsin the oncoming flow that is the ratio of the distance Hf of the inletfrom the inner wall of the fan duct (undisturbed flow line Fu) to thetotal radial distance Hi of the inlet. This distance is less than orequal to (that is, not greater than) seventy percent (Hf/Hi≦0.70). Thepenetration ratio is the ratio of the exposed radial height Hf of theinlet to the height of the fan duct Hfd and is not greater than fifteenpercent (Hf/Hfd≦0.15) and, in one embodiment, not greater than tenpercent (Hf/Hfd≦0.10). The aspect ratio is the ratio of the width W ofthe heat exchanger inlet (see FIG. 4) divided by the height to the outerwall Hf of the inlet in the radial direction and is less than fifty (50)percent and in one embodiment, less than twenty (20) percent.

FIG. 4 is a perspective view of a portion of the heat exchanger system52 referred to as the inlet and outlet module 108.

As shown in FIG. 3 and FIG. 4, the inlet 58 includes a first side 112and a second side 114 at the intersection of the inlet plane P with theinlet-outlet module. A first sidewall 116 and a second sidewall 118extend from the inner wall 98 and the outer wall 102 of the inlet 58.The sidewalls extend in the upstream direction to the inner wall 36 ofthe fan duct 32. Each sidewall decreases in height in the upstreamdirection until it reaches the inner wall of the fan duct. An inlet ramp122 is a curved wall that extends forwardly in the upstream directionfrom the inner wall of the inlet to the inner wall of the fan duct. Theinlet ramp extends circumferentially between the sidewalls to define asmooth transition from the fan duct into the inlet.

The inlet 58 has a mass flow ratio characteristic which is no greaterthan seventy-five percent (MFR≦0.75) under all operative conditions ofthe engine. The mass flow ratio characteristic for a particularoperative condition of the engine is defined for the inlet at the firstcovered section at the inlet plane P and is the actual flow through thefirst covered section into the heat exchanger flow path divided by theproduct of the density and velocity of the free stream flow multipliedby the area of the first covered section. In one particular embodiment,the MFR was approximately fifty (50) percent under all operativeconditions.

As mentioned, the inner duct 76 extends from the inlet 58. The innerwall of the inlet duct extends from the inner wall 98 of the inlet. Theouter wall of the duct extends from the outer wall 102 of the inlet.Each of the walls separately converges radially toward the axis Ar inthe downstream direction to create a sudden drop below the undisturbedline of flow Fu of the working medium gases.

The inlet and outlet module 108 has sidewalls 116,118 extendingrearwardly which are a continuation of the first sidewall and the secondsidewall. A flow path wall 124 extends between the sidewalls 116,118 andrearwardly to the lobed mixer 94 from the outer surface 104 of the outerwall 102 at the first covered section. The inlet has a width W whichextends between the sidewalls at the inner wall and is constant for theinlet. The inlet-outlet module 108 has a width Wo at the outlet 62 whichextends between the first sidewall and the second sidewall. The width Wois greater than the width W. The aspect ratio of the outlet is theheight Ho of the outlet divided by the width Wo and is less thantwenty-five (25) percent and, in one embodiment, less than twenty (20)percent. A first circumferentially extending surface 126 extends fromthe first sidewall 116 and a second circumferentially extending surface128 extends from the second sidewall 118 to define the inner wall 98 ofthe fan bypass duct 32 between the fan struts 44. These surfaces alsoprovide references for the undisturbed flow line Fu. A strut profileshape is formed in each of the circumferentially extending surfaces toadapt the inlet-outlet module to abuttingly engage the fan strut whichis partially broken away for clarity in FIG. 2.

As shown in FIG. 5, the ratio of the height Hi of the lobed mixer 94 tothe spaced apart distance of the mixer Hp from the inner wall is one.The lobed mixer is formed of a plurality of lobe peaks 132 that areconcave with respect to the exhaust flow. Each lobe peak is spacedcircumferentially one from the other. A plurality of lobe valleys 134are disposed inwardly of and joined to the lobe peaks. The lobe valleysare convex to the exhaust flow path 56 of the heat exchanger system andconcave 34 to the working medium flow path. Each lobe valley extendsbetween a pair of lobe peaks to define a plurality of axially extendingchannels 136 that also extend radially inwardly. The channels 138 forthe exhaust flow path of the heat exchanger system only extend axiallyrearwardly.

During operation of the gas turbine engine 10 shown in FIG. 1, workingmedium gases are flowed along the primary flow path 28 and the secondaryflow path 34 for working medium gases. Heat is transferred from variouscomponents to the cooling fluid which is flowed along the flow path 74to the heat exchanger 54. Cooling air is flowed along the flow path 56from the fan duct 46 continuously through the heat exchanger under alloperative conditions of the engine. The flow path for the heat exchangersystem extends through the inlet 58 including the inlet duct 76, thefirst and second conduits 82,84 to the heat exchanger and through theoutlet 64. The flow path 56 is uninterrupted under all operativeconditions. No valving is required to modulate the flow. This provides asimple system for cooling, avoiding the cost, complexity and weightassociated with supplying valves and controlling the valves to such aheat exchanger system.

Under operative conditions, an adverse static pressure gradient existsbetween axial locations on the inner wall 36 of the fan duct havingundisturbed lines of flow Fu, that is locations whose flow is notdisturbed by the heat exchanger system 52. Cooling air is passed throughthe inlet 58 to the system at the inner wall of the fan duct. Asmentioned, the inlet has a mass flow ratio characteristic at the inletwhich is no greater than seventy-five percent (MFR≦0.75) and, in oneembodiment, was slightly less than fifty percent (MFR≦0.50). Inaddition, the radial height Hi of the inlet is greater than the wallflow characteristic Bu. As a result, flow entering the heat exchangerexperiences a static pressure rise sufficient to the drive flow throughthe heat exchanger system. Total pressure recovery is high because theheight Hi of the inlet is greater than the wall flow characteristicheight Bu. The length Lid of the inlet duct 76 provides for mixing ofany separated flow that occurs at the inlet. This enables a furtherpressure recovery in the form of a static pressure rise at thatlocation.

The rise in static pressure at the inlet 58 drives the captured gasesalong the flow path 56 for the heat exchanger system 52. Flow occurseven though an adverse static pressure gradient exists in the fan duct46 along an undisturbed flow line between the inlet 58 and outlet 62.This enables construction of a heat exchanger system having a relativelyshort length (in one embodiment, about one foot) as compared with thoseheat exchanger systems which must rely on a static pressure differencealong an undisturbed flow line in the fan duct between the inlet axiallocation and the outlet axial location (several feet) or as compared toconstructions that use a low pressure compartment as a sump for gasesdischarged from the working medium flow path. In addition, the sidewalls116, 118 of the inlet ramp 122 block side flow from the ramp andpreserve the static pressure rise that is beginning to occur at the rampof the inlet 58.

Another advantage of the present design and method of operating theengine is the level of drag experienced caused by the heat exchangersystem 52 projecting into the working medium flow path. The aspect ratioof the heat exchanger inlet is not greater than twenty percent and theoutlet is not greater than twenty-five percent. In addition, theprojection ratio of the heat exchanger system into the flow path is notgreater than ten percent of the height of the working medium flow path.This results in acceptable levels of drag and a concomitantly small lossin energy as the working medium gases 34 in the fan bypass duct 32 sweepby the inlet and outlet module 126 of the heat exchanger system 52.

In addition, the low aspect ratio and projection ratio of the inlet andoutlet module 126 into the working medium flow path 34 decreases thepossibility of foreign object damage and ingestion. This reduces thepossibility of blockage of the heat exchanger with ice and other debrisearlier ingested into the working medium flow path of the engine ascompared to designs having a greater projection ratio and a largeraspect ratio for the inlet. The ramp 22 and inlet duct 76 provide asudden drop below the undisturbed flow line Fu at the inlet 58. Thiscauses the foreign objects in the mainstream flow adjacent the flowentering the inlet to sweep past the inlet to the heat exchanger system.In addition, the inlet is disposed at the inner wall 36 of the fan duct.Foreign objects are generally centrifuged outwardly with a greaterincidence of foreign object damage occurring in the region above a tenpercent projection than within a ten percent projection by the inletinto the fan duct. Thus, the inlet is greater in size than the wall flowcharacteristic Bu but small enough so that many foreign objects willsweep by the inlet.

Ice is a particular problem occurring at high altitude operation or asthe aircraft passes through hail and ice storms. Chunks of ice that havea diameter greater than the projection of the inlet into the fan duct 32will strike the entrance to the fan duct and fragment at the inlet 58.The region of the outer wall of the inlet has increased thickness ofabout four to six times the thickness of interior walls.

The method of operating the engine 10 includes passing the cooling airof the heat exchanger flow path 56 through the inlet 58 and ducting thecooling air sharply downward to impede the ingestion of foreign objectsas mentioned above. It also causes foreign objects, such as ice, tostrike the walls 79 and other structure, such as the vanes 82, boundingthe flow path and to fragment on the interior of the inlet duct 76 andin the first conduit 80 in the heat exchanger cavity 66. For example,these particles will strike the inlet guide vanes 82 to the heatexchanger as the particles move radially inwardly and, if moving withsufficient momentum, may strike the bottom of the cavity prior tostriking the inlet to the heat exchanger which avoids damage to the moredelicate structure of the heat exchanger.

Another advantage of having the flow path extend sharply inwardly andsharply outwardly as compared to the axial length of the ducts is thecompactness of the heat exchanger system. The heat exchanger inlet andoutlet module has a length of about one foot for one embodiment. Thelength to height ratio of the system is about one (L/H<0.9-1.1).

After the cooling air is heated in the heat exchanger 54, the heated airis flowed radially outwardly through the second conduit and into theexhaust passage 86. The first portion 88 extends radially outwardly andthe second portion 92 extends axially in the downstream direction todirect rearwardly the exhausted gases from the heat exchanger. Theexhaust gases from the heat exchanger flow path 56 encounter the lobedmixer 94. Operation of the engine includes mixing these heated exhaustgases 46 with the cooler working medium gases from the fan duct. Thelobed mixer promotes the mixing, ensuring that the energy from the gasesenters the working medium flow path where it usefully increases thrustheat adjacent structure, such as might occur in constructions where heatis transferred to metal plates which shield the composite wall of thenacelle and which is then transferred to other locations of the engine.These heated gases increase the energy of the gas stream and, in oneembodiment, make up for the loss in energy caused by flowing the gasesthrough the heat exchanger flow path.

Another advantage is the durability of downstream structure 64 thatresults from the lobed valleys 136 of the mixer 94 that are directedradially inwardly. The lobed valleys duct air having a dynamic head orvelocity head (one half density multiplied by the square of thevelocity) which is much greater than the dynamic head of the heated air56 being exhausted from the heat exchanger system 52. In oneconstruction, the dynamic head of the working medium gases is four timesgreater than the dynamic head of the heat exchanger system gases. As aresult, the flow path gases 34 drive inwardly into the exhaust gases 56,providing a screen of cool air to the structure rearwardly of the heatexchanger system 52. This screen of air blocks the gases from the heatexchanger from contacting the wall with curtains of cool air adjacentthe wall. This avoids over-temperaturing any adjacent compositestructure 64, such as the sound absorbing structure, and avoids thenecessity for metal protective shields disposed in the flow path toprotect such structure from over-temperature conditions.

A particular advantage of the modular construction of the heat exchangerinlet and outlet is the method by which the inlet and outlet module 108may be quickly and efficiently formed. The inlet and outlet module is acast construction. Use of the casting technique is enhanced by therelatively small size of the casting. The cast construction allows forprecisely contoured passages and for a robust construction at criticallocations as compared with devices which might be formed of thin sheetmetal. In addition, the casting ensures the relationship between theflow path and the aerodynamic inlet meets the requirements of theaerodynamic design. The design provides for easy replacement in case ofinjury to the inlet and outlet module.

Fabricating the inlet and outlet module as a casting has otheradvantages. For example, the complex shape of the flow paths are easilyformed time after time. This avoids the need for many different kinds oftooling to form the complex shapes associated with sheet metal work andwelding of the sheet metal sections.

Another advantage of a cast module for the inlet and outlet is thestrength-to-weight ratio of the design. Casting allows for differentthickness material at different locations for the inlet and outletmodule enabling the module to have thicknesses tailored so that it isthicker at the leading edge and other locations where needed, such asinlet and outlet wall and the sides, and with thinner walls with ribs inlocations where the strength is not needed to resist foreign objectdamage or for other requirements. In addition, the casting is in aone-piece construction having an overall stiffness of the structure thatis greater than if the part were made from many pieces.

The one-piece construction is also lighter in weight, eliminatingflanges needed to attach parts together in constructions of made ofseveral components whether the components are cast or welded sheetmetal. An aerodynamic advantage results by eliminating steps or gapsthat occur between components and that cause aerodynamic losses. Thecritical aerodynamic alignment between the outlet 58 and the inlet 62are maintained.

Finally, the modular inlet and outlet design provides for ease ofinstallation of one or more of the modules within the engine. Forexample, some engine constructions have a first inlet and outlet modulewhich is in flow communication with a first heat exchanger and a secondinlet and outlet module which is in flow communication with a secondheat exchanger. Either of these modules is easily replaced or easilyremoved to permit inspection of the heat exchanger cavity for blockageand for foreign object damage should the engine have passed throughsevere hailstorms. Finally, an advantage in installation and removal ofthe module is the interchangability of modules because the design is acast one-piece construction that maintains alignment between the exitand inlet.

Although the invention has been shown and described with respect todetailed embodiments thereof, it should be understood by those skilledin the art that various changes in form and detail thereof may be madewithout departing from the spirit and the scope of the claimedinvention.

What is claimed is:
 1. An inlet outlet module for a heat exchangersystem for a gas turbine engine that is disposed about an axis ofrotation Ar, the engine having a primary annular flow path for workingmedium gases disposed about the axis Ar and a secondary annular flowpath for working medium gases disposed about the primary flow path, thesecondary flow path having a fan duct which is bounded by wallsincluding an inner wall, an outer wall, a radial bifurcator wallextending between the inner wall and the outer wall, the secondary flowpath further having lines of flow extending along such walls whichinclude flow lines Fd disturbed by the heat exchanger system and flowlines Fu undisturbed by the heat exchanger system, the inlet and outletmodule having a pair of axially spaced surfaces which are coincidentwith the undisturbed flow line Fu, which comprises:an inlet having afirst covered section at an inlet plane P havingan inner wall extendingfor a width W which is inwardly of the undisturbed flow line Fu, anouter wall which extends circumferentially a width W, which is spacedrearwardly from and radially outward from the inner wall of the inlet byan inlet radial height Hi, and radially outward from the undisturbedflow line an exposed radial height Hf, the inlet having an exposureratio which is the ratio of the exposed radial height Hf to the inletradial height Hi and which is not greater than seventy percent(Hf/Hi≦0.7), and the inlet having an aspect ratio which is the ratio ofan exposed radial height Hf to the width W of the inlet which is notgreater than one half (Hf/W≦0.50); an outlet having an exhaust passagewhich is spaced axially from the inlet and terminating at an outletsection, the outlet having an outermost wall which is radially outwardlyof the undisturbed flow line a maximum radial height Ho and having awidth Wo and having an aspect ratio which is not greater than one-half(Ho/Wo≦0.50); a first sidewall and a second sidewall which extend fromthe outlet section to the outer and inner walls of the inlet and a flowpath surface wall which forms the outermost portion of the outletextends between the sidewalls and extends from the outlet section to theouter wall of the inlet; wherein the module is a one piece casting andhas an inlet having a thickness adjacent the outer wall of the inletwhich is at least four times the thickness of adjacent walls on theinterior of the module, the module having acceptable levels of drag andforeign object damage tolerance which results in part from the exposureratio of less than seventy percent and the aspect ratio of less thanfifty percent.
 2. The heat exchanger system for a gas turbine engine asclaimed in claim 1 wherein the aspect ratio is not greater thantwenty-five percent (Hf/W≦0.25).
 3. The heat exchanger system for a gasturbine engine as claimed in claim 1 wherein the system includes aninlet duct extending from the inlet plane P which is in flowcommunication with the inlet, the inlet duct having a length Lid and afirst inner wall and a second outer wall, the inner wall of the ductextending from the inner wall of the inlet, the outer wall of the ductextending from the outer wall of the inlet lip, each separatelyconverging radially toward the axis Ar in the downstream direction tocreate a sudden drop below the undisturbed flow line Fu.
 4. The heatexchanger system for a gas turbine engine as claimed in claim 2 whereinthe system includes an inlet duct extending from the inlet plane P whichis in flow communication with the remainder of the inlet, the inlet ducthaving a length Lid and a first inner wall and a second outer wall, theinner wall of the duct extending from the inner wall of the inlet, theouter wall of the duct extending from the outer wall of the inlet lip,each separately converging radially toward the axis Ar in the downstreamdirection to create a sudden drop below the undisturbed flow line Fu. 5.The heat exchanger system for a gas turbine engine as claimed in claim 1wherein the inlet further includes an inlet ramp which extends in theupstream direction from the inner wall of the inlet to the inner wall ofthe fan duct.
 6. The heat exchanger system for a gas turbine engine asclaimed in claim 5 wherein the inlet has a first side wall and a secondside wall which extend from the axial location of the inner wall to theouter wall and bound the ramp, the side walls decreasing in height inthe upstream direction to the inner wall of the fan duct whereinsidewalls help preserve the rise in static pressure which occurs on theramp upstream of the first covered section.
 7. The heat exchanger systemfor a gas turbine engine as claimed in claim 1 wherein cooling air isexhausted from the heat exchanger system under operative conditions andwherein the outlet further has a mixer which extends upstream from theoutlet section, the mixer having a plurality of inwardly extendingchannels which are adapted to flow working medium gases from the flowpath for the fan duct with a radially inward component of velocitytoward the inner wall of the fan duct to mix the working medium gaseswith the cooling air exhausted from the heat exchanger system andwherein the mixer avoids unacceptable heating of adjacent downstreamstructure of the heat exchanger system and increases thrust of theengine by intermixing the heated gases from the flow path of the heatexchanger with the working medium gases to increase the energy of theworking medium gases.
 8. The heat exchanger system for a gas turbineengine as claimed in claim 7 wherein the mixer has a plurality of lobepeaks that are concave with respect to the exhaust flow, each spacedcircumferentially one from the other and a plurality of lobe valleysinwardly of the lobe peaks that are convex with respect to the exhaustflow path of the heat exchanger system and concave with respect to theworking medium flow path, each lobe valley extending between a pair oflobe peaks to define a plurality of axially extending channels, thechannels for the exhaust flow path of the heat exchanger systemextending rearwardly and the channels for the fan duct flow pathextending radially inwardly.
 9. The heat exchanger system for a gasturbine engine as claimed in claim 1 wherein a first circumferentiallyextending surface extends from the first sidewall and a secondcircumferentially extending surface extends from the second sidewall todefine the inner wall of the fan duct and wherein each of thecircumferentially extending surfaces adapt the inlet-outlet module toabuttingly engage radial structure in the fan duct.